Ebola viruses pose a significant threat to US military forces and the general population, particularly in areas endemic areas of equatorial Africa. This NIAID Category A biodefense pathogen is a potential biological threat agent and unpublished reports indicate that the former Soviet Union attempted to weaponize this family of viruses. Of all the species of Ebola virus, Zaire virus (EBOV) and Sudan virus (SUDV) have caused the greatest number of outbreaks and account for 94% of all Ebola virus-related deaths. Since there are no approved preventative vaccines or therapeutics for Ebola virus infections, supportive care remains the only option for treating Ebola virus infected patients. Historically, antibody immunotherapy as a post-exposure treatment for Ebola virus infection was largely ignored due primarily to numerous failed attempts to protect non-human primates (NHPs) from Ebola virus challenge. Recent successes by several independent groups have provided convincing evidence that antibody-based immunotherapies can be an effective countermeasure against Ebola virus infection. In fact, several monoclonal antibody (mAb) cocktails targeting EBOV have proven efficacious in NHP models. However, there is currently a lack of research efforts dedicated to developing SUDV-specific antibody-based immunotherapies. This is particularly concerning considering the causative agent of three of the last four Ebola virus outbreaks has been SUDV. Our proposal is designed to address the void in SUDV-specific therapeutics by developing antibody-based immunotherapeutics that target SUDV specifically. Leveraging existing SUDV-specific mAb and scFv libraries, we will generate murine-human chimeric mAbs from select lead-candidate mAbs and scFvs and produce these SUDV-specific mAbs using plant and mammalian-based expression systems. Producing SUDV-specific mAbs in plant and mammalian systems will provide a renewable source of de-immunized SUDV-specific antibody-based immunotherapies and allow a direct performance comparison of mAbs from each expression system. Plant and mammalian-derived SUDV-specific mAbs will be evaluated for in vitro antigen specificity and virus neutralization before entering in vivo protective efficacy trias. Efficacy studies in mice will be used to down-select the best three SUDV-specific mAbs to move forward into NHP efficacy trials. Pharmacokinetic evaluation and post-exposure efficacy testing will be completed for our SUDV-specific mAb cocktail with the intent of developing optimal dosing and treatment regimens and defining the therapeutic window. The objective of our proposal is to develop an antibody-based immunotherapy for the treatment and management of Sudan virus infection. This effort directly addressed a gap in the current Ebola virus therapeutics portfolio and, if successful, will provide an effective countermeasure against Sudan virus that is positioned for IND-enabling studies.